MODELING ZERO SINK NUTRIENT-UPTAKE BY ROOTS WITH ROOT HAIRS FROM SOIL- COMPARISON OF 2 MODELS

The influence of root hairs on nutrient uptake from soil is incorporat ed in uptake models using two different methods, In both models, the r oots and root hairs are assumed to behave as a zero sink, hence all nu trient that is transported to the absorbing surface is taken up. The t ransport of nutrient is assumed to be by diffusion only, In the first model, the continuity equation for zero sink uptake by roots is extend ed with a separate sink term for zero sink influx into root hairs, and root hair influx is computed using an approximate analytical solution , In the other model, the diffusion equation in three dimensions is so lved, with boundary conditions that impose zero sink uptake behavior o n the root with root hairs, Model calculations of phosphate uptake at phosphorus-deficient growth conditions were performed with both models , Differences in computed uptake were attributable to the use of the a pproximate analytical solution for root hair influx. The difference in cumulative uptake after 10 days at different buffering, root hair den sity, and root hair length computed with the two models was generally less than 15%, Calculations with the three-dimensional model showed th at very short root hairs (0.08 mm) may hinder the diffusion of nutrien t to the root, resulting in reduced uptake compared with uptake by a r oot without root hairs.